Refrigeration system and apparatus for operating at partial loads



y 21, 1954 w. L. M GRATH ETAL 3,141,311

REFRIGERATION SYSTEM AND APPARATUS FOR OPERATING AT PARTIAL LOADS Filed Jan. 14, 1965 2 Sheets-Sheet l INVENTORS.

WILLIAM L. MC GRATH.

FIG. I STANLEY J. RACHFALI WILLIAM E. CLARK.

7 7% Al IORNEY.

y 21, 1954 w. MCGRATH ETAL 3,141,311

REFRIGERATION SYSTEM AND APPARATUS FOR OPERATING AT PARTIAL LOADS;

Filed Jan. 14, 1963 2 Sheets-Sheet 2 FIG. 3

INVENTORS. WILLIAM L. MC GRATH. STANLEY J. RACHFAL, WILLIAM E. CLARK.

ATTORNEY.

United States Patent 3,141,311 REFRIGERATHON SYSTEM AND APPARATUS FOR GPIERATING AT EARTIAL LGADS William L. McGrath, itanley J. Rachfal, and William E. Clark, Syracuse, N.Y., assigners to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Jan. 14, 1963, Ser. No. 251,291 3 Claims. (Cl. 62-510) This invention relates generally to refrigeration apparatus as used in cooling large buildings employing a centrifugal refrigeration machine wherein refrigerant gas from the evaporator is compressed and discharged into the condenser to be changed into its liquid state. More particularly, this invention pertains to an economy cycle of reduced load operation during the intermediate seasons when the outside wet bulb is low and apparatus therefor, to obtain substantial refrigeration with the centrifugal compressor inoperative and to improve performance when the centrifugal compressor is operative.

In operating refrigeration machines of the kind under consideration, it frequently requires running under partial loads and this is especially so whenever the temperature of the water circulating through the condenser for the purpose of cooling the refrigerant therein is less than the temperature of the medium to be cooled in the evaporator. This condition is prevalent during the intermediate seasons and results in a reduced volume of vaporous refrigerant generated in the evaporator because of the small load thereon. It is possible that this reduced volume may become so insuflicient that it could induce a reversal of the gaseous refrigerant fiow through the compressor and result in intermittent operation.

Another problem which arises from the reduced volume of vaporous refrigerant is the unstable operation of the constant speed centrifugal compressor. When the suction volume falls below the design point, the compressor may surge rendering the operation inefficient and it is highly possible that this would cause serious damage. Surging occurs when operation is in a region in which the compressor pressure-volume characteristic curve shows an increase in pressure with an increase in volume rate of flow. As the compressor approaches the surge condition, the output pressure fluctuates at first rather gently and then very violently. This later condition is accompanied by excessive outlet temperatures, reversal of flow of gas in the discharge line, noise and excessive vibrations which may strain the compressor blades and ultimately cause fatigue failure.

Various means have been devised to overcome the above situations, arising from partial loading which maintains stable operation so that the refrigerant cycle continues to be unidirectional in the desired manner by providing a sufficient volume of vaporous refrigerant to the evaporator to keep above the surge limit of the compressor. One such arrangement is described in United States Patent No. 2,888,809 to Rachfal, wherein a hot gas bypass line, having a valve therein, is located between the condenser and the evaporator, or suction line, and provides pressure differentials required for an efiicient refrigerant cycle.

Other systems for controlling the compressor capacity at partial loading employ a variable speed cocmpressor motor, variable drives, or inherently variable steam turbines.

The above methods and apparatus all increase the cost of the air conditioning equipment for operation in the intermediate seasons when the cooling load is actually low or only about 30 percent of design capacity. Furthermore, in all the foregoing systems, there remains the need, and the great expense, of running the centrifugal compressor to obtain the reduced cooling required.

It is, therefore, the primary object of our invention to provide an improved centrifugal refrigeration system (and apparatus) employing the heat exchangers in the condenser and in the evaporator or cooler to produce the required refrigeration without using the centrifugal compressor, eliminating its expensive operation.

Another object of our invention is to increase the heat transfer efiiciency of the evaporator or cooler under partial loads.

It is also an object of our invention to provide an accessory package to a centrifugal refrigeration machine that will enable more efficient partial load operations to be obtained.

It is a further object of our invention to provide an accessary arrangement of the kind described wherein refrigerant is recycled in spray form for the purpose of increasing partial load operation efiiciency.

It is a still further object of our invention to provide an accessary unit of the type under consideration wherein a double pumping action is provided in order to more efficiently recycle refrigerant in spray form during partial load operation.

It is a still further object of our invention to provide a spray system producing a vaporous cloud of refrigerant in'the evaporator or cooler.

It is also the object of our invention to furnish a source of liquid refrigerant, in the condenser, available to the spray system during the intermediate season operation and to the hot gas bypass line during normal periods of operation.

A further object of our invention is to recirculate an amount of refrigerant vapor through the evaporator without operating the centrifugal compressor.

The solution to the above problems arising from partial load operation in a conventional refrigeration machine is accomplished in our invention by including a spray system above the chilled water tubes in the evaporator to raise the foam level therein to the design point wetting those upper tubes normally not participating in the heat exchange during partial loading with a cloud of refrigerant. As used in this application, the term cloud of refrigerant is defined as a mixture of gaseous and atomized liquid refrigerant. The sprays in this system are operated by means of a small standard reciprocating compressor recycling refrigerant gas through the evaporator to produce substantial refrigeration without running the centrifugal compressor.

A liquid source from the condenser is also connected to the spray system and the gas emanating from the reciprocating compressor, induces liquid refrigerant in atomized form into the evaporator at the low pressure required therein.

A specific embodiment of our invention has been selected to illustrate the aforementioned objects and further objects, as well as advantages, which will become apparent from the ensuing specification and drawings herein below set forth in which:

FIGURE 1 is a diagrammatic view of a standard centrifugai refrigeration system modified with the addition of the vaporous spray system of our invention.

FIGURE 2 is an enlarged partial view of the vaporous spray system of our invention as incorporated into the evaporator or cooler section.

FIGURE 3 is a partial view of the system showing the condenser as modified toprovide liquid refrigerant flow to the vaporous spray system of our invention.

Referring particularly to the drawings wherein like reference numerals indicate corresponding portions throughout, there is shown in FIGURE 1 a diagrammatic View of a refrigeration machine equipped with the vaporous spray system illustrating our invention. A

conventional centrifugal compressor 11 is of the type well known in refrigeration systems and is driven by a prime mover, such as a directly coupled constant speed motor 13. Refrigerant gas is compressed by the compressor 11 and passes through a discharge line 15 to a shell and tube type condenser 17 wherein cooling water, circulating through a tube bundle 19, extracts heat from the gas converting it to liquid form.

In normal operation employing the centrifugal compressor 11, the liquid from the condenser 17 passes through a liquid line 21 into a float chamber 23 having a valve therein controlling the liquid passage. The liquid then passes into a shell and tube type cooler or evaporator 25 wherein a chilled water load, such as used for the cooling medium in air conditioning system, circulates through a tube bundle 27 in heat exchange relation with the refrigerant liquid surrounding the tubing. As heat from the Water is absorbed by the cooled refrigerant liquid, refrigerant vapor is produced and rises through an eliminator section 29, located in the upper portion of the cooler 25 over the tube bundle, which prevents the passage of any entrained liquid, returning it to the liquid pool, and passes the hot refrigerant gases into a suction line 31 leading to the inlet side of the centrifugal compressor 11 thus completing the refrigerant cycle. It is therefore apparent that the refrigerant liquid flows from the higher pressures in the condenser 17 to the lower pressures in the cooler or evaporator 25 through a float chamber 23.

A modification of the basic cycle described above employs a hot gas bypass conduit 33 connecting the upper portions of the condenser 17 and cooler 25, with a valve 35 controlling the volume of gas flow. A liquid line 37, including a control valve 39, permits a flow of liquid refrigerant from the condenser 17 to the conduit line 33, downstream from the valve 35 restriction, for desuperheating the hot gases being bypassed to the lower pressures required. This modification is fully described in United States Patent No. 2,888,809 to Rachfal and further description thereof is deemed unnecessary. This modified cycle assures a suflicient volume of vaporous refrigerant to prevent a reversal of flow in the system during periods of reduced loads. However, this operation is with a semi-flooded cooler, which is not only inefiicient, but is also expensive due to the required running of the centrifugal compressor 11.

, In partial load operation with a semi-flooded cooler or evaporator 25 the invention herein contemplated comprises an accessory package forming a spray system and includes a small reciprocating compressor 41, which recirculates refrigerant gases through the cooler 25. This compressed gas emanating from the compressor 41 is employed to induce a volume of refrigerant liquid into the cooler 25 and actually produces a vaporous cloud of refrigerant therein which will wet the exposed tubing 27 and thereby increases the heat transfer eiiiciency by also raising the foam level in the cooler 25. Accordingly, a secondary suction line 43 is provided connecting the inlet side of the reciprocating compressor 41 to a refrigerant gas source leaving the cooler 25. In this embodiment, line 43 is shown in FIGURE 1 connected into the bypass conduit 33, but it can also be connected into the main suction line 31 or directly into the cooler at any point above the eliminator section 29. A secondary discharge line 45 passes the compressed recirculated gas from the compressor 41 into a primary distribution header 47, centrally adjacent to and inside the cooler 25 (FIGURES 1 and 2). A secondary liquid line 49, including a control valve 51, permits a flow of liquid from the condenser into a secondary distribution header 53 located inside the cooler and adjacent to the primary header 47.

The design of the vaporous spray system of our invention is based upon utilizing a high energy, but a limited quantity, of gas provided by the reciprocating compressor 41 to effectively motivate a large amount of the liquid from the condenser. It is best shown by FIGURE 2, wherein a plurality of primary nozzles 55, aflixed in the header 47, jets the compressed gas into associated secondary nozzles 57, affixed in the header 53. The nozzles 57 have a bell-shaped inlet and a long intermediate circular mixing tube that gradually transforms into a fiat elliptical discharge end. This construction insures a proper mixing of the gas and liquid from headers 47 and 53 respectively and introduces a fanned out spray of vaporous refrigerant for optimum tube bundle coverage at the low pressures required. To cover a 15 foot length of header, there should be twenty-nine of such nozzle units at a distance of 6 inches apart. With a 10 HP. and 40 c.f.m. reciprocating compressor, it is possible to carry the spray a distance of 4 feet at an elevation of 3 inches. This point represents the center of gravity of the overlapping spray patterns. In order to accommodate the spray pattern, the eliminator section 29 is elevated at the one end adjacent the sprays, as shown in FIGURE 1, and a baffle 59 is provided on the other end near the bypass connection to prevent any liquid carryover. The gas distribution header 47 is arranged outside of the liquid distribution header 53 in our preferred embodiment for structural reasons and to reduce the condensation loss of high pressure refrigerant in contact with the cooled liquid, but it could well be placed inside. The discharge line 45 (FIGURE 1) is looped to above the liquid level in the condenser for the purpose of preventing any of the liquid from draining into the reciprocating compressor 41 and causing damage thereto.

FIGURE 3 shows the condenser 17 as improved by our invention. We prefer the condenser as the source of stored refrigerant liquid available to the spray system of this invention. A weir 61 is provided at the bottom of the condenser shell with a bafile 63, located above the normal outlet to the main liquid line 21, to direct the liquid condensing on the tube portions thereabove into a liquid pool 65 formed within the weir section. The arrangement of the weir 61, as shown, is such that most all the liquid produced under partial load operation in the condenser'25 is routed to the spray system, however, other weir locations may be employed. The weir location is limited only by the additional quantity of refrig erant charge required to operate the spray system herein contemplated for the purpose of increasing partial load operation efiiciency.

Under normal load operating conditions, valve 51 is closed, valve 39 is fully open, while valve 35 is partially open to suit the compressor surge free volume load requirement. In addition a double throw control switch 67 is closed to interlock a power source 69 to the compressor motor 13 through a circuit 71 and prevent operation of the small reciprocating compressor 41 at the same time. The liquid from the condenser will fill the lefthand side section of the condenser shell as shown in FIGURE 3, and overflowing the weir 61, it will eventually reach the float chamber 23 by way of the main liquid line 21. At the same time, the pool of liquid 65 will serve as a source of liquid through line 37 for the hot gas bypass desuperheating purpose in conduit line 33 Under the partial load operation of our invention, valves 35 and 51 are fully open and valve 39 is closed. The switch 67 is thrown to interlock the power source 69 to the motor of the small compressor 41 through a circuit 73 which will also turn off the compressor motor 13. Thus it is apparent that in this preferred embodiment it is impossible to operate both compressors at the same time. 1 Approximately two-thirds of the liquid produced will enter the spray system (shown by FIGURE 2) and one-third of the liquid will enter the float chamber 23 once equilibrium conditions are established. Prior to this, however, We make it possible to use the refrigerant liquid stored in the condenser 17 which enters the cooler 25 to further improve the heat transfer conditions of the latter by raising the static liquid level over the entire tube bundle 27. It is also apparent that the spray system herein contemplated may be employed in an arrangement wherein all the valves 35, 39, and 51 are partially opened to suitable positions thereby achieving an increased efiiciency due to the improved heat transfer in the cooler 25. For such an arrangement a new switching means (not shown) must be provided to replace the double throw switch 67 and such that will enable the operation of both compressors at the same time. We prefer to operate solely with the small reciprocating compressor 41 to afford an economy refrigerant cycle without operating the large centrifugal compressor 11.

It will also be apparent from the above description that we have invented a system wherein the heat transfer of the cooler is maintainable at maximum efliciency, whenever the cooling load on the refrigeration system is reduced, and have further afforded an economy cycle of operation, whenever the outside wet bulb temperature falls below the design point of the main system. In a proposed application of our system involving two 3,300 ton refrigeration machines, the predicted performance curves indicate that over -l,000 tons of almost free cooling can be obtained from each machine, when the conditions are right, operating at approximately 30 percent of capacity without running the large centrifugal compressors.

While we have described a preferred embodiment of the invention, it will be understood the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

We claim:

1. In a refrigeration machine including a centrifugal compressor, a prime mover driving the centrifugal compressor, a condenser, a discharge line connecting the compressor and the condenser, a cooler having a chilled water tube bundle therein, a suction line connecting the evaporator and the compressor, a bypass line connecting the condenser to the cooler for the purpose of supplying additional volume of gas to the suction line, a control valve in said bypass line, an accessory cooling system for partial loading comprising:

(a) a refrigerant liquid header within said cooler adjacent one side above the chilled water tubes,

(b) a plurality of elongated mixing tubes centrally aflixed in spaced relation to said header with a bevellcd end section inside the header and a flat elliptical discharge end section outside the header projecting into said cooler,

(c) a refrigerant gas header juxtaposed said liquid header on the same center line and inside said cooler,

(d) a plurality of short tubes atfixed one end in spaced relation within said gas header on the same centers as said mixing tubes and with high velocity jet nozzles in the other end extending within the bevelled end sections of said mixing tubes,

(e) a refrigerant gas supply line connected into said gas header,

(f) a refrigerant liquid supply line connected into said liquid header,

(g) a valve in said liquid supply line controlling the flow of liquid therethrough,

(h) a weir in the bottom of said condenser providing a reservoir of refrigerant liquid,

(i) a drain connection in said condenser connecting into the reservoir of refrigerant liquid and connected on one side by said refrigerant liquid supply line,

(i) a second refrigerant liquid supply line including an intermediate valve controlling refrigerant flow and connecting said condenser drain connection to said bypass line above said control valve between the condenser and the cooler,

(k) a second refrigerant gas supply line connected to said bypass line between said control valve and the bypass line connection into said cooler, and

(l) a small reciprocating compressor with the suction side connected to said second gas supply line and the discharge side connected to said gas header supply line.

2. In a refrigeration system, the combination of a centrifugal compressor, a condenser, a cooler having tubing therein, a discharge line connecting the centrifugal compressor and the condenser, a suction line connecting the cooler and the centrifugal compressor, and an accessory cooling system for partial load operation when operation of the centrifugal compressor is discontinued including a bypass conduit connecting the cooler and the condenser to forward gaseous refrigerant from the cooler to the condenser, control means in the bypass conduit, an auxiliary compressor, spray means in the cooler above the tubing to discharge a vaporous cloud of refrigerant over the tubing, means placing the auxiliary compressor in communication with the gaseous side of the cooler to pass gaseous refrigerant from the cooler to the auxiliary compressor, a discharge line connecting the spray means with the auxiliary compressor, a liquid line connecting the spray means with the condenser, and control means to discontinue operation of the centrifugal compressor and to actuate the auxiliary compressor thereby shutting down the centrifugal compressor under low load conditions and utilizing the auxiliary compressor to supply required refrigeration.

3. A refrigeration system according to claim 2 in which the means placing the auxiliary compressor in communication with the gaseous side of the compressor comprise a line connecting the auxiliary compressor with the bypass conduit between the cooler and the control means in the bypass conduit.

References Cited in the file of this patent UNITED STATES PATENTS 2,159,251 Brizzolara May 23, 1939 

2. IN A REFRIGERATION SYSTEM, THE COMBINATION OF A CENTRIFUGAL COMPRESSOR, A CONDENSER, A COOLER HAVING TUBING THEREIN, A DISCHARGE LINE CONNECTING THE CENTRIFUGAL COMPRESSOR AND THE CONDENSER, A SUCTION LINE CONNECTING THE COOLER AND THE CENTRIFUGAL COMPRESSOR, AND AN ACCESSORY COOLING SYSTEM FOR PARTIAL LOAD OPERATION WHEN OPERATION OF THE CENTRIFUGAL COMPRESSOR IS DISCONTINUED INCLUDING A BYPASS CONDUIT CONNECTING THE COOLER AND THE CONDENSER TO FORWARD GASEOUS REFRIGERANT FROM THE COOLER TO THE CONDENSER, CONTROL MEANS IN THE BYPASS CONDUIT, AN AUXILIARY COMPRESSOR, SPRAY MEANS IN THE COOLER ABOVE THE TUBING TO DISCHARGE A VAPOROUS CLOUD OF REFRIGERANT OVER THE TUBING, MEANS PLACING THE AUXILIARY COMPRESSOR IN COMMUNICATION WITH THE GASEOUS SIDE OF THE COOLER TO PASS GASEOUS REFRIGERANT FROM THE COOLER TO THE AUXILIARY COMPRESSOR, A DISCHARGE LINE CONNECTING THE SPRAY MEANS WITH THE AUXILIARY COMPRESSOR, A LIQUID LINE CONNECTING THE SPRAY MEANS WITH THE CONDENSER, AND CONTROL MEANS TO DISCONTINUE OPERATION OF THE CENTRIFUGAL COMPRESSOR AND TO ACTUATE THE AUXILIARY COMPRESSOR THEREBY SHUTTING DOWN THE CENTRIFUGAL COMPRESSOR UNDER LOW LOAD CONDITIONS AND UTILIZING THE AUXILIARY COMPRESSOR TO SUPPLY REQUIRED REFRIGERATION. 